13C-Proline and 2H-L-glutamic acid were injected intracerebroventricularly and the incorporation of the label from these compounds into proline and/or glutamate examined. The maximal incorporation of label into striatal proline occurred 10 min after injection. However, no label was observed in glutamate. The maximal incorporation of label from 2H-L-glutamate occurred within 5 min and declined thereafter. The amount of label was 3 fold higher in the septum than cortex, striatum or hippocampus.